The present invention relates generally to intraocular irrigation/aspiration devices.
Occurrence of the disease known as cataracts, in which the lens of the eye becomes clouded, is common, and can lead to blindness. It has become accepted practice to alleviate this condition by surgically removing the cataract-affected lens and replacing it by an artificial intraocular lens.
The cataract-affected lens is usually removed by manual extraction or phaco-emulsification. Manual extraction requires expression of the nucleus of the lens through a wound of about 12 mm in length. The residual peripheral lens material is then removed by an intraocular irrigation/aspiration device.
The technique known as phaco-emulsification, as described, for example, in U.S. Pat. No. 3,589,363, enables removal of the cataract-affected lens through a much smaller incision of about 2.5-4 mm, for example, 3.2 mm. This is accomplished using high frequency ultrasound energy, typically of 40 kHz frequency, that is transmitted by a phaco-emulsification needle to fragment or emulsify the nucleus of the cataract-affected lens. Once fragmented or emulsified, the nuclear material is aspirated through a lumen of the phaco-emulsification needle.
Japanese patent application No. 80-38451 describes a phaco-emulsification tip having a reduced diameter portion proximal of the tip face that reduces the suction flow rate and allows shortening of the overall length of the tip.
WO 94/22402 describes a phaco-emulsification method and tip wherein the tip is configured to enhance generation of shockwaves and/or focussing of shockwaves. Some embodiments of phaco-emulsification tip includes a lumen having a diameter smaller than the diameter of the opening at the distal endface of the tip.
An improved phaco-emulsification needle is also described and claimed in Austrialian patent application No. 33365/95 (International Patent Application No PCT/AU95/00558), in the name of the present applicant, wherein the needle includes a mid-region portion having a plurality of outwardly extending projections forming longitudinally-oriented grooves. The grooves ensure adequate cooling of the needle in the vicinity of the entry wound, thereby reducing the risk of thermal damage to tissue in the vicinity of the entry wound. Some embodiments of that invention include reduced-diameter portions to accommodate the presence of the longitudinally-oriented grooves.
After the nuclear material of the lens has been aspirated or emulsified by use of the phaco-emulsification needle and aspirated through a lumen thereof, there remains in the eye residual lens material which is derived from softer lens material which originally surrounded the nucleus.
After treatment with the phaco-emulsification needle it is necessary to remove the residual lens material by means of an intraocular irrigation/aspiration device. This device includes a tip which is inserted through the incision in the eye. The tip includes a small opening at its distal end which opening is about 0.3 mm in dimension. A lumen leads from the opening through the device to an aspiration device. Further, the device includes an outer sleeve which extends to a point adjacent to the tip to form an external conduit which is connected to a supply of fluid.
There is no need to apply energy to the intraocular irrigation/aspiration device as the lens nucleus has already been fragmented or emulsified during phaco-emulsification. The device is connected to an aspirator which applies suction to the lumen and hence to the opening at the tip. In this way residual lens material is drawn through the opening and then along the lumen so as to remove the residual lens material from the interior of the eye. Simultaneously, fluid is fed through the external conduit to the interior of the eye to replace the aspirated fluid and maintain the volume of fluid and pressure within the chamber of the eye.
In operation of the intraocular irrigation/aspiration device, it is important to ensure that there is a balance between infusion and aspiration of fluids so as to maintain stable pressure and volume within the intraocular chambers. This reduces the likelihood of inadvertent aspiration of structures such as the iris, or the delicate posterior capsule which divides the eye into anterior and posterior chambers. The posterior capsule is liable to rupture if engaged by the aspiration port which may result in loss of the vitreous gel which fills the posterior chamber of the eye. An intact capsule is also important to support a posterior chamber intraocular lens implant, and therefore inadvertent rupture of the posterior capsule is a serious complication which may result in an unsatisfactory technical result and a poor visual outcome from cataract surgery. It has been found that the distal opening or port of the tip of the aspiration device sometimes becomes transiently blocked or occluded during aspiration such as by a relatively large piece of residual lens material. This leads to a temporary increase in vacuum within the lumen which is relieved when the blocking material is eventually drawn through the opening with equalisation of pressure within the chamber of the eye and the aspiration device. However, this equalisation of pressure can induce a surge of fluid along the lumen and a transient reduction in pressure and volume within the pressure of the eye or chamber instability. It is important that adequate infusion of fluid is available to counteract the reduction in pressure and volume.
An outer sleeve of the irrigation/aspiration device may be formed from rigid plastic or metal which resist deformation by the incision. A rigid sleeve however, increases leakage from the wound reducing pressure within the eye, and the ability to maintain a stable chamber volume of fluid. A soft outer sleeve is better able to seal the incision and reduce wound leakage. A tight sealed incision however, may compress a soft sleeve and reduce the flow and infusion of the irrigating fluid into the eye which is necessary to replace aspirated fluid and maintain a stable chamber with respect to pressure and volume.
The present invention provides an intraocular irrigation/aspiration device in which the aspiration of fluid and lens material is regulated and the post occlusion surge phenomenon is reduced.
In accordance with one aspect of the present invention there is provided an intraocular irrigation/aspiration device including a hollow shaft having first and second ends, a tip at the first end of the shaft, said tip including an opening and a lumen extending from the opening to the second end of the shaft, wherein the lumen has a portion of reduced internal cross-sectional area over at least part of its length.